Method of and system for locating a position

ABSTRACT

A method of and system for locating a position in which a plurality of frequency standard devices based on the action of the natural frequencies associated with transitions between energy states in atoms and/or molecules are synchronized or phase compared at the same initial location. Two of three frequency standard devices, in a two-dimensional embodiment, are placed at transmitting stations on a known baseline. The third device is at a third station, a receiving station, which receives signals from the two transmitting stations. At each transmitting station, means are provided for producing and transmitting a radio frequency carrier signal of fixed frequency and of fixed phase under the control of the frequency standard device associated with the respective station. The radio frequency carrier signals produced at the different transmitting stations differ in frequency. The radio frequency carrier signal produced at each transmitting station is modulated with a modulating signal produced under the control of the same frequency standard device which controls the means which produce the radio frequency carrier. At the receiving station, means are provided for producing a reference signal corresponding to the modulating signal and two radio frequency signals corresponding, in frequency, to the radio frequency carrier signals transmitted, the means at the receiving station being controlled by the frequency standard device associated with the receiving station. The reference signal is compared at the receiving station with the modulating signals recovered from the radio frequency carriers to determine respective time differences, the differences representing coarse position data from which the total number of phase rotations (full lanes) the receiving station is from each of the transmitting stations are determined. The phase relationships between each of the received radio frequency carrier signals and the respective one of the two radio frequency signals produced at the receiving station are determined, the relationships representing fine position data which are measurements of the receiving station position within a given phase rotation (lane). Methods and systems for locating a position in three dimensions are also described. The fine ranges, distances within given lanes, are respectively added by a computer to respective coarse ranges, each of which represents the total number of lanes to the full lane closest to respective ones of the transmitting stations, the totals being the distances between the receiving station and each of the transmitting stations.

United States Patent [191 Elwood METHOD OF AND SYSTEM FOR LOCATING APOSITION [76] Inventor: Albert A. Elwood, PO. Box 10592,

Riviera Beach, Fla. 33404 Notice: The portion of the term of this patentsubsequent to Oct. 12, 1988, has been disclaimed.

[22] Filed: Oct. 4, 1971 [21] Appl. No.: 186,206

Related U.S. Application Data [63] Continuation-impart of Ser. No.833,638, June 16,

1969, Pat. NO. 3,613,095.

[52] U.S. Cl 343/112 D [51] Int. Cl G0ls 5/14 [58] Field of Search343/112 C, 112 D, 102; 235/150.27

[56] References Cited UNITED STATES PATENTS 2,924,820 2/1960 Dishal etal 343/112 D 3,325,811 6/1967 Earp 343/112 D 3,613,095 10/1971Elwood.... 343/112 D 3,150,372 9/1964 Groth 343/112 D 3,237,196 2/1966Hampton 343/112 D Primary ExaminerBenjamin A. Borchelt AssistantExaminerDenis H. McCabe [57] ABSTRACT A method of and system forlocating a position in which a plurality of frequency standard devicesbased on the action of the natural frequencies associated withtransitions between energy states in atoms and/0r molecules aresynchronized or phase compared at the same initial location. Two ofthree frequency standard devices, in a two-dimensional embodiment, areplaced at transmitting stations on a known baseline. The third device isat a third station, a receiving station, which 1 ains:

[ 1*Mar. 12, 1974 receives signals from the two transmitting stations.At each transmitting station, means are provided for producing andtransmitting a radio frequency carrier signal of fixed frequency and offixed phase under the control of the frequency standard deviceassociated with the respective station. The radio frequency carriersignals produced at the different transmitting stations differ infrequency. The radio frequency carrier signal produced at eachtransmitting station is modulated with a modulating signal producedunder the control of the same frequency standard device which controlsthe means which produce the radio frequency carrier. At the receivingstation, means are provided for producing a reference signalcorresponding to the modulating signal and two radio frequency signalscorresponding, in frequency, to the radio frequency carrier signalstransmitted, the means at the receiving station being controlled by thefrequency standard device associated with the receiving station. Thereference signal is compared at the receiving station. with themodulating signals recovered from the radio frequency carriers todetermine respective time differences, the differences representingcoarse position data from which the total number of phase rotations(full lanes) the receiving station is from each of the transmittingstations are determined. The phase relationships between each of thereceived radio Trequency carrier signals and the respective one of thetwo radio frequency signals produced at the receiving station aredetermined, the relationships representing fine position data which aremeasurements of the receiving station position within a given phaserotation (lane). Methods and systems for locating a position in threedimensions are also described. The fine ranges, distances within givenlanes, are respectively added by a computer to respective coarse ranges,each of which represents the total number of lanes to the full laneclosest to respective ones of the transmitting stations, the totalsbeing the distances between the receiving station and each of thetransmitting stations.

34 Claims, 22 Drawing Figures LEASE ERROR COORDNATES DESIRED =05 oNPATENTEBIIARIZ IsTI 3.797.015

SHEET 02 0F 16 FIG. IB

STATION 8 STATION C ALTI METER ALTITUDE STATION D (SATELLITE) RBASE 2STATION 0 FIG. ID

I STATION B RBASE l STATION A PAIENTED m \2 1974 sum 03 0F 16 INVENTOR.ALBERT A. ELWOOD iUOJU 0:20.74

PATENTEUHAR 12 I974 SHEET 05 HF 16 ALBERT A. ELWOOD PATENIEDIARIE NM3797.015

SHEET 09 DF T6 FIG. 8

DETECTED REFERENCE (0) -j DETECTED ADRB'DRD (d) l DIFFERENTIATEDREFERENCE (e) 7 DIFFERENTTATED AORBORD (f) y A CLIPPED a INVERTED IREFERENCE 9 CLIPPED a INVERTED (h) I A OR B 0R D START STOPIIIIIIIIIIIIIIIIIIII COUNT REPRESENTS COARSE RANGE 76 I I N AN 111W WTZERO LINE EXCLUSIVE (n) CROSSING 77 OR REFERENCE DETECTDR GATE STARTGENERATOR PULSE CLOCK COUNTER I l 82 SHAPER f I (k) STOP NW NW zERD LINEEXCLUSIVE (0) W CROSSING 83 (m) OR RESET- DETECTDR GATE 84 PULSEGENERATOR Pmmmm 12 m4 3.791015 SHEET 10 0F 16 ||||||ss REFERENCE)lllllllllllllllllllliii N0-NOTCH AORBORDM llllllllllllllllllllliiNO-NOTCH REFERENCE X-OR (n) I I AORBORDX-0R(o) coum START (p) coum STOPi RESET m E i i COUNTER (s) Illllllllllllllllllllllll coum REPRESENTSCOARSE RANGE FIG. IO

FIG. I5

I23 {I24 |25 ATOMIC FREQUENCY TRANSM'TTER' cw smug ism V (A) m MHZ (I26[I27 TIMING cmcun MODULATOR F |2a [I30 m ATOMIC FREQUENCY TRANSMmR Cl(g)CK SYNTEESIZER (B) 3305 MHZ [I32 1 |33 TIMING CIRCUIT MODULATORPATENTEDIIIIRI2 IITTI 3.791015 SHEET 11 HF 16 es se ,8? ,OO

ATOMIC FREQUENCY 3.5O5OMN CLOCK OATE TRANSMITTER SYNTHESIZER ZERO LINEZERO LINE CROssINC CROssINC GATE DETECTOR DETECTOR K 88 FREQUENCY ANDGATE sYNTIIEsIzER a CONTROL PULSE TIMER A CIRCUIT 94 FIG. II

| I I K 67 i 68 70 K I FLIP-FLOP PULSE RECEIVER (a) LIMITER (c) 7 AND(8) CLAMPER SHAPER I72 STOP START COUNTER F [8 (f) C Sl bwG I76 IDETECTOR RESET CLOCK FREQUENCY (b) (d) LINITER SYNTHESIZER I73 [I77 I78If I79 ATOMIC FREQUENCY ZEROL'NE (g) mm m 7 CROSSING CLOCK sYNTIIEsIzERDETECTOR COUNTER PATENIEIJMATTTZTQM sum 13 or 16 20 205 {L206 ATOM'CFREQUENCY CLOCK I TRANSMITTER (A) SYNTHESIZER m2 MHZ FREQUENCY 83WFREQUENCY SYNTHESIZER MODULATOR I205 BISEC I ITSEC f4 TIMING n n nATOMIC CIRCUIT (ZIO CLOCK (B) FREQUENCY SYNTHESIZER FREQUENCYTRANSMITTER SYNTHESIZER TIMING I0 SEC.

CIRCUIT FIG. I3

METHOD OF AND SYSTEM FOR LOCATING A POSITION This application is acontinuation-in-part application of my co-pending application Ser. No.833,638 filed June 16, 1969, now US. Pat. No. 3,613,095, dated Oct. 12,1971 entitled Method of and Apparatus for Locating a Position.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates in general to position locating and in more particularity to amethod and system for accurately locating a specific position.

Although both the method and the system are of general utility they areespecially useful in offshore oil surveys where it is important that aspecific location be accurately and precisely identified. In anoperation such as an offshore oil survey two transmitting stations wouldbe land-based whereas a receiving station would be located on anoffshore vessel which can be moved to an exact location which is beingsought.

2. Description of the Prior Art Many phase or time comparison systemshave been developed for locating a position and are in use today. Thereare those based on the radar principle in which an echo or return ofsignal technique is used; there are those based on the use oftransponders where receipt and retransmission of a signal are utilized;and there are those based on the Loran principal where time differencein the receipt of two transmitted pulses define a hyperbolic line ofposition.

SUMMARY OF THE INVENTION Due to the high stability of atomic clocks,which are accurate on the order of one part in or 10 no continuoussynchronization between stations is required once the initialsynchronization among three atomic clocks is performed or the initialphase/time relationships among the three atomic clocks are established.

The frequency of an atomic clock is determined by atomic particle ormolecular vibrations and thereby remains constant. Its accuracy is about100 to 1,000 times as great as that of the quartz clock in which thevibration frequency changes in the course of time. Due to the constancyof the frequency of an atomic clock a new and novel system of positionlocating has been discovered.

Coarse range is defined as the total number of phase rotations at thecarrier frequency (wave lengths) over the distance between eachtransmitting station and the receiving station, measured to the nearestfull phase rotation in a direction along the transmitting stationradials toward each transmitting station. Full phase rotations (wavelengths) or even fractions thereof may be further defined as lanes.

Fine range is defined as the position of the receiving station within agiven phase rotation, or lane, measured in a direction along thetransmitting station radials toward each transmitting station.

Coarse and fine ranges are combined in a computer to determine thedistance to each transmitting station from the receiving station.Because of this, the system may be defined as a range-range system. Thecomputer further may convert the ranges into position with respect toany grid or geographic reference that may be desired.

It is the principal object of the invention to provide a method of and asystem for locating a position in which frequency standard devices areused to provide coarse and fine position data which representrespectively coarse and fine ranges.

It is an additional object of the invention to provide a method of and asystem for locating a position in which frequency standard devices attransmitter locations are used to produce radio frequency carrier waveswhich are phase compared with signals produced at a receiving station,under the control of a frequency standard device, to provide fineposition data, and modulation signals, under the control of thefrequency standard devices at the transmitter locations, are placed onthe radio frequency carriers, recovered at the receiving station andcompared with corresponding signals produced at the receiving station,under the control of the frequency standard device at the receivingstation, to provide coarse position data.

A further object of the invention is to provide a method of and a systemfor position locating in which atomic clocks or the like are utilized toprovide modulated constant frequency signals having constant knownabsolute phase relationships with one another; the received signals arethen converted into distance data by determining the phase differencesof the constant frequency signals and differential positions ofrecovered modulation signals using a plurality of signals from an atomicclock.

Another object of the invention is to provide a position locating systemin which no continuous synchronization between stations is required onceinitial synchronization is performed or phase relationships among atomicclocks established.

A still further object of the invention is to provide a positionlocating method and system in which the signal transmissions are singlepath and do not require an echo and/or retransmission.

Yet another object of the invention is to provide a position locatingsystem in which atomic clocks or the like are utilized to provide aplurality of signals having known phase relationships with one anotherand a plurality of pulse or frequency change signals having known timeor phase relationships with one another to develop respectively fine andcoarse position information.

A still further object of the invention is to provide a method of and asystem for locating a position in three dimensions using threetransmitting stations, controlled by frequency standard devices, and areceiving station which also uses a frequency standard device to providesignals for comparison with signals received from the transmittingstations.

Still another object of the invention is to provide a method of and asystem for locating a position in three dimensions using threetransmitting stations, controlled by frequency standard devices, and areceiving station which also uses a frequency standard device to providesignals for comparison with signals received from the transmittingstations, at least one of the transmitting stations being carried by asatellite.

Further features, objects, and advantages will either be specificallypointed out or become apparent when, for a better understanding of theinvention, reference is made to the following written description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. IA is a diagrammatic viewillustrating the use of a method and system, in a two-dimensionalarrange ment, according to the invention;

FIG. 1B is a diagrammatic pictorial view illustrating the use of amethod and system, in a three-dimensional arrangement, according to theinvention in which three transmitting stations are used;

FIG. 1C is a diagrammatic pictorial view illustrating the use of amethod and system, in a three-dimensional arrangement, according to thepresent invention in which two transmitting stations are used inconjunction with an altimeter which can be carried on an aircraft or thelike;

FIG. 1D is a diagrammatic pictorial view illustrating the use ofa methodand system, in a three-dimensional arrangement, according to the presentinvention in which three transmitting stations are used, one of thembeing carried by a satellite;

FIG. 2 is a block diagram of an illustrative embodiment of one of thetransmitting stations of the system;

FIG. 3 is a block diagram of an illustrative embodiment of one of thereceiving stations of the system;

FIG. 4 is a block diagram in greater detail of part of a typicalreceiving station; the two sheets of the drawing containing FIG. 4 areto be placed end-to-end to illustrate a complete station including acomputer;

FIG. 5 is a block diagram of an illustrative embodiment of a notchmodulated transmitting station suitable for use in a system according tothe invention;

FIG. 6 is a simplified illustrative block diagram of a portion of areceiving station suitable for use in a system according to theinvention in conjunction with notch modulated transmitting stations ofthe type illustrated in FIG. 5;

FIG. 7 is a block diagram of a time comparator suitable for use as thetime comparator associated with the portion of a receiving stationillustrated in FIG. 6;

FIG. 8 shows a number of waveforms which are useful in understanding theoperation of the time comparator illustrated in FIG. 7;

FIG. 9 illustrates a preferred embodiment of a time comparator which maybe used as part of a modified embodiment of the receiver shown in FIG.6;

FIG. 10 shows a number of waveforms which are useful in understandingthe operation of the time comparator illustrated in FIG. 9;

FIG. 11 is a block diagram of an illustrative embodiment of a frequencyshift keyed transmitter which is particularly suitable for use inanother preferred embodiment of the invention;

FIG. 12 is a simplified block diagram of a portion of a receivingstation usable in a system including frequency shift keyed transmittersconstructed as shown in FIG. 11;

FIG. 13 is a block diagram of illustrative embodiments of two frequencymodulated transmitter stations, suitable for use in a further embodimentof the invention;

FIG. 14 is a block diagram of an illustrative embodiment of a receivingstation usable in a system including frequency modulated transmittersconstructed as shown in FIG. 13;

FIG. 15 is a simplified block diagram of illustrative embodiments of twotransmitter stations which are particularly suitable for use in apreferred embodiment of the invention in which a heterodyne principle isused;

FIG. 16 is a simplified block diagram of an illustrative embodiment of aportion of a receiving station usable in a preferred embodiment of thesystem in which a heterodyne principle is used;

FIG. 17 is a block diagram of an illustrative embodiment of a phasecomparator usable in a locked heterodyne apparatus forming part of theportion of the receiving station shown in FIG. 16;

FIG. 18 is a simplified block diagram of an embodiment of a preferredphase comparator for developing fine distance data usable as part of thereceiving station forming part of the invention; and

FIG. 19 shows a number of waveforms which are useful in understandingthe operation of the phase comparator illustrated in FIG. 18.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1A of thedrawings, a system according to the invention will include atransmitting station A which is placed at a known position, atransmitting station B which is placed at a known position, with A and Bplaced on a known baseline R and a receiving station C which is at anunknown position and becomes the measured or located position.

As illustrated in FIG. 18, a three-dimensional system according to theinvention may include a transmitting station A, a transmitting station Band a transmitting station D each placed at a respective location,spaced from one another. Stations A and B are placed on a known baselineR and stations B and D are placed on a known baseline R A receivingstation C, illustrated as being carried by a moving aircraft, is at anunknown position and becomes the measured or located position.

As shown in FIG. 1C, a three-dimensional system according to theinvention may comprise a transmitting station A which is placed at aknown position, a transmitting station E which is placed at a knownposition, stations A and B being positioned on a known baseline R and areceiving station C shown as being carried by a moving aircraft which isat an unknown position. The aircraft carries as part of its equipment analtimeter.

As illustrated in FIG. ID, a further three-dimensional system accordingto the invention may include a transmitting station A, a transmittingstation B and a transmitting station D each positioned at respectivelocations, spaced apart from one another. Stations A and B are placed ona known fixed baseline R 1 and stations B and D are placed on a knownbaseline R As illustrated, station D is carried by a satellite which maybe either a synchronized satellite or an unsynchronized satellite havinga predictable orbit and known position at a given time. A receivingstation C, illustrated as being carried by a moving aircraft, is at anunknown position and becomes the measured or located position.

The two transmitting stations illustrated here as shore-based stations Aand B (FIGS. 1A and 1C) and transmitting stationsA, B and D (FIGS. 18and ID) are illustrated in greater detail in FIG. 2. The station shownis duplicated at A and B or A, B and D with the only essentialdifference being that different RF frequencies are transmitted fromrespective stations.

An atomic clock provides a high frequency signal, for example 9 GH whichis utilized in two ways. The high frequency signal is fed to frequencysynthesizer l 1 where it is reduced in frequency to a selected frequencyin a range suitable for transmission over distances of up to about 100miles, in an exemplary system, and for accuracy of phase determination.The range may be, for example, from about 1.0 to about 5.0 MH Thefrequency synthesizer 11 converts the high frequency signal, from clock10 to one in the lower range (1.0 5.0 MH while maintaining the stabilityof the primary standard from clock 10. The output of frequencysynthesizer 11 which is extremely accurate in its phase and frequencycharacteristics is fed to driver synthesizer 12 wherein it is amplifiedto a level sufficient to drive highly stable radio transmitter 13. Theradio transmitter 13 is provided with an antenna from which a radiofrequency signal of given frequency within the selected range and ofprecise phase and frequency is transmitted. Thus, the stability andaccuracy of clock 10 is preserved and reflected in the radiated signal.

The high frequency signal from clock 10 is also fed to a frequencysynthesizer 14 wherein it is converted to a given signal in theabove-mentioned suitable lower range, for example from about 1.0 MH, toabout 5.0 MP1,. Frequency synthesizer 14, like synthesizer 11, preservesthe accuracy and stability of clock 10 and reflects the accuracy thereofin its own output which is coupled, as a synchronizing signal, to timeformat generator or pulse timer 15. Pulse timer 15 produces a train ofpulses which are very accurately positioned with respect to one another.The pulses may be positioned, for example, at 10 second intervals.

The pulses from pulse timer 15 are fed to amplitude modulator 16 which,in turn, is arranged to modulate transmitter 13. It will be appreciatedthat other types of modulation could be used. For example, frequencyshift keying could be provided, notch modulation could be used, and insome applications, a tone signal could be used to modulate transmitter13 in either amplitude or frequency.

The modulations appearing on carrier signals from transmitting stationsA, B and D (FIGS. 1B and 1D) or A and B (FIGS. 1A and 1C) are utilizedat a moving receiving station C (FIGS. lA-lD) to produce coarse positioninformation data, and the phase relationships of the radio frequencysignals from the transmitting stations are utilized to produce fineposition information.

The signal from radio transmitter 13 at station A (FIG. 1A) is receivedby the receiver 17 (FIG. 3) while the signal from radio transmitter 13at station B (FIG. 1A) is received by the receiver 18 (FIG. 3). Radiofrequency output signals from receivers 17 and 18 are fed to phasedetermining units 20 and 21, respectively, each of which compares thephase of respective radio frequency signals with the phase of the radiofrequency signals from frequency synthesizers 29 and 31 which have theirrespective inputs coupled to atomic clock 19. The phase differencestranslated into digital signals, A phase A and A phase B, representativeof phase difference are fed into the range computer 24 of the computersection 27 of the system and converted into two range signals indicatingfine position information within a particular lane which may, forexample, be 720 feet wide. Each degree of relative phase rotation in theexample represents two feet. Of course, the outputs of phase determiningunits 20 and 21 do not provide lan e identification.

Each of the receivers 17 and 18 is provided with amplitude demodulators,not shown, which develop pulse signals which are fed to pulse timecomparators 23 and 22, respectively. Each of pulse timers 22 and 23compares the time of occurrence of each of the pulse signals with thetime of occurrence of pulses in a train of pulses fed to each pulse timecomparator 22 and 23 from frequency synthesizer and pulse timer 41 whichhas its input coupled to the atomic clock 19. The pulse time comparatorsprovide output coarse range digital signals R and R which are also fedinto range computer 24, the output of which is coupled to computer 25which provides output signals R and R repre senting the accuratedistance station C is from each of the stations A and B, as illustratedin FIG. 1A.

The position computer 25 operates the position keeper and display 26which converts the two ranges from shore stations A and B into precisionposition in any selected coordinate system. Signals R0,; and R0,, may beeither digital or analog signals and the position keeper and display maybe either digital or analog or both. The atomic clock 19 is providedwith a timing output signal I which is used to synchronize computer 27as illustrated generally by timing inputs t which are provided bycount-down circuits, not shown, which are driven by timing signal tAlternatively, timing signal t could be directly fed into the computer27 provided that computer 27 contained suitable count-down circuits.

FIG. 4 illustrates in greater detail the instrumentation used in theoffshore station when the system is being used to locate an offshoreposition.

Phase determining unit 20 of FIG. 3 is shown, in FIG. 4, as comprised ofa phase comparator 30. Phase determining unit 21 of FIG. 3 is shown inFIG. 4 as comprised of a phase comparator 32.

Frequency synthesizers 33 shown in FIG. 4 correspond to frequencysynthesizers 29 and 31 shown in FIG. 3 and frequency synthesizer andpulse timer 42 correspond to frequency synthesizer and pulse timer 41shown in FIG. 3.

In the embodiment illustrated in FIG. 4, the function of the two pulsetime comparators 22 and 23 illustrated in FIG. 3 is performed by asingle pulse time comparator 34 which has its pulse inputs fromreceivers 17 and 18 and provided via a multiplexer 43, and its outputsrepresentative of coarse ranges A and B data fed to computer 27 viade-multiplexer 44.

Digital outputs from phase comparators 30 and 32 are fed respectively todigital range computers 35 and 36 as fine position data, while outputsfrom pulse time comparator 34 are fed respectively to digital rangecomputers 35 and 36 as coarse position data.

The two digital range computers 35 and 36 process their respective datainputs to provide output signals representing the fine (accurate) rangeof station C from stations A and B respectively.

The outputs from digital range computers 35 and 36 are fed to digitalposition computer 37 associated with data storage apparatus 39 whichprovides baseline and w shore base station information. Using storedinforma-

1. A position locating system comprising a first source of a signal ofgiven frequency and given phase, a second source of a signal of saidgiven frequency and a predetermined phase relationship with said givenphase, a third source of a signal of said given frequency and apredetermined phase relationship with said given phase, means controlledby said first source for transmitting a first radio signal from a firstpoint including first modulating means controlled by said first sourcefor periodically notch modulating said first radio signal with a firsttime signal, means controlled by said second source for transmitting asecond radio signal from a second point including second modulatingmeans controlled by said second source for periodically notch modulatingsaid second radio signal with a second time signal, means controlled bysaid third source for generating a signal having a frequency identicalto that of said first radio signal and a signal having a frequencyidentical to that of said second radio signal at a third point, meanscontrolled by said third source for periodically producing timereference signals, means for receiving said first radio signal and saidsecond radio signal at said third point, first phase comparing means atsaid third point for comparing the phase of the received first radiosignal with that of said signal having a frequency identical to that ofsaid first radio signal, second phase comparing means at said thirdpoint for comparing the phase of the received second radio signal withthat of said signal having a frequency identical to that of said secondradio signal, means at said third point for demodulating said first andsaid second radio signals to recover said first time signal and saidsecond time signal, and means for comparing respectively said first timesignal and said second time signal with said time reference signals. 2.A position locating system according to claim 1 wherein said firstsource, said second source and said third source are respectively first,second and third atomic clocks.
 3. A position locating system as claimedin claim 1 including computer means for receiving output signals fromsaid first phase comparing means, said second phase comparing means andsaid means for comparing respectively said first time signal and saidsecond time signal with said time reference signals for providing outputsignal data representative of the distance the third point is from thefirst and second points.
 4. A position locating system as claimed inclaim 3 including means controlled by said computer means for storingand displaying said output signal data.
 5. A position locating systemaccording to claim 1 wherein said means at said third point fordemodulating said first and said second radio signals are means fordetecting notch modulation to recover said first time signal and saidsecond time signal.
 6. A position locating system according to claim 1comprising a fourth source of signal of said given frequency and apredetermined phase relationship with said given phase, means controlledby said fourth source for transmitting a third radio signal from afourth point including third modulating means controlled by said fourthsource for periodically notch modulating said third radio signal with athird time signal, means for receiving said third radio signal at saidthird point, means controlled by said third source for generating asignal having a frequency identical to that of said third radio signal,third phase comparing means at said third point for comparing the phaseof the received third radio signal with that of said signal having afrequency identical to that of said third radio signal, means at saidthird point for demodulating said third radio signal to recover saidthird time signal, and means for comparing said third time signal withsaid time reference signals.
 7. A position locating system according toclaim 6 wherein said means at said third point for demodulating saidthird radio signal is a means for detecting notch modulation to recoversaid third time signal.
 8. A position locating system according to claim6 including computer means for receiving output signals from said firstphase comparing means, said second phase comparing means, said thirdphase comparing means, said means for comparing respectively said firsttime signal and said second time signal with said time reference signalsand said means for comparing said third time signal with said timereference signals for providing output signal data representative ofdistance said third point is from the first, second and fourth points.9. A position locating system as claimed in claim 8 including meanscontrolled by said computer means for storing and displaying said outputsignal data.
 10. A position locating method comprising providing a firstsignal of given frequency and given phase, providing a second signal ofsaid given frequency and a predetermined phase relationship with saidgiven phase, providing a third signal of said given frequency and apredetermined phase relationship with said given phase, periodicallynotch modulating a first radio signal related to said first signal witha first time signal also related to said first signal, transmitting thefirst radio signal from a first point, periodically notch modulating asecond radio signal related to said second signal with a second timesignal also related to said second signal, transmitting the second radiosignal from a second point, generating a signal having a frequencyidentical to that of said first radio signal and a signal having afrequency identical to that of said second radio signal at a thirdpoint, generating time reference signals related to the third signal atthe third point, receiving said first radio signal and said second radiosignal at said third point, demodulating said first radio signal andsaid sEcond radio signal to recover said first time signal and saidsecond time signal, comparing the phase of the received first radiosignal with that of said signal having a frequency identical to that ofsaid first radio signal, comparing the phase of the received secondradio signal with that of said signal having a frequency identical tothat of said second radio signal, and comparing respectively therecovered first time signal and the recovered second time signal withsaid time reference signals.
 11. A position locating method according toclaim 10 wherein said first signal, said second signal and said thirdsignal are respectively provided from first, second and third atomicclocks.
 12. The position locating method according to claim 10 includingproviding a fourth signal of the given frequency and a predeterminedphase relationship with said given phase, periodically notch modulatinga third radio signal related to said fourth signal with a third timesignal also related to said fourth signal, transmitting the third radiosignal from a fourth point, receiving said third radio signal at saidthird point, generating a signal having a frequency identical to that ofsaid third radio signal at said third point, demodulating the receivedthird radio signal to recover said third time signal, comparing thephase of the received third radio signal with that of said signal havinga frequency identical to that of said third radio signal, and comparingthe recovered third time signal with said time reference signals. 13.The position locating method according to claim 12 wherein the step ofdemodulating said third radio signal is the step of demodulating thereceived notch modulated third radio signal to recover said third timesignal.
 14. A position locating system comprising a plurality of sourcesof signals of given frequency and predetermined phase relationships,means controlled respectively by each of said plurality of sources fortransmitting from respective points respective signals includingmodulating means controlled respectively by each of said plurality ofsources for notch modulating said respective signals with respectivetime signals, means controlled by a source of signal having the samegiven frequency as said plurality of sources of signals and having apredetermined phase relationship for generating signals corresponding tosaid respective signals at an additional point, means controlled by saidsource of signal at said additional point for producing time referencesignals, means for receiving said respective signals at said additionalpoint, phase comparing means at said additional point for comparingrespectively the phase of each of said respective signals as receivedwith the phase of the signals corresponding to said respective signals,means at said additional point for demodulating said respective signalsas received to recover said respective time signals, and means forcomparing the recovered respective time signals with said time referencesignals.
 15. A position locating system according to claim 14 whereinsaid plurality of sources of signals are two sources of signals and therespective points are two points.
 16. A position locating systemaccording to claim 14 wherein said plurality of sources of signals arethree sources of signals and the respective points are three points. 17.A position locating system according to claim 16 wherein at least one ofsaid plurality of sources of signals is carried by a satellite.
 18. Aposition locating system according to claim 16 wherein said source ofsignal at said additional point is carried by an aircraft.
 19. Aposition locating system according to claim 15 wherein said source ofsignal at said additional point is carried by an aircraft, said aircrafthaving an altimeter.
 20. A position locating method comprising providinga first plurality of signals of given frequency and predetermined phaserelationships, deriving a second plurality of signals from said firstplurality of signals, notch modulating said second plurality of signalswith time signals derived respectively from said first plurality ofsignals, transmitting from respective points said second plurality ofsignals, receiving at an additional point said second plurality ofsignals, providing a source of signal at said additional point havingthe same frequency as said given frequency and having a predeterminedphase relationship, generating signals corresponding to said secondplurality of signals under the control of the source of signal at saidadditional point, generating reference time signals under control ofsaid source of signal at said additional point, comparing the phase ofeach of the received second plurality of signals with the phase of thesignals corresponding to said second plurality of signals, demodulatingsaid second plurality of signals to derive said time signals, andcomparing the derived time signals with the reference time signals. 21.A position locating system comprising a first source of a signal ofgiven frequency and given phase, a second source of a signal of saidgiven frequency and a predetermined phase relationship with said givenphase, a third source of a signal of said given frequency and apredetermined phase relationship with said given phase, means controlledby said first source for transmitting a first radio signal from a firstpoint including first modulating means controlled by said first sourcefor periodically pulse modulating by pulsing said first radio signalwith a first time signal, means controlled by said second source fortransmitting a second radio signal from a second point including secondmodulating means controlled by said second source for periodically pulsemodulating by pulsing said second radio signal with a second timesignal, means controlled by said third source for generating a signalhaving a frequency identical to that of said first radio signal and asignal having a frequency identical to that of said second radio signalat a third point, means controlled by said third source for periodicallyproducing time reference signals, means for receiving said first radiosignal and said second radio signal at said third point, first phasecomparing means at said third point for comparing the phase of thereceived first radio signal with that of said signal having a frequencyidentical to that of said first radio signal, second phase comparingmeans at said third point for comparing the phase of the received secondradio signal with that of said signal having a frequency identical tothat of said second radio signal, means at said third point fordemodulating said first and said second radio signals to recover saidfirst time signal and said second time signal, and means for comparingrespectively said first time signal and said second time signal withsaid time reference signals.
 22. A position locating system according toclaim 21 wherein said first source, said second source and said thirdsource are respectively first, second and third atomic clocks.
 23. Aposition locating system comprising a first source of a signal of givenfrequency and given phase, a second source of a signal of said givenfrequency and a predetermined phase relationship with said given phase,a third source of a signal of said given frequency and a predeterminedphase relationship with said given phase, means controlled by said firstsource for transmitting a first radio signal from a first pointincluding first modulating means controlled by said first source forperiodically frequency modulating said first radio signal with a firsttime signal, means controlled by said second source for transmitting asecond radio signal from a second point including second modulatingmeans controlled by said second source for periodically frequencymodulating said second radio signal with a second time signal, meanscontrolled by said third source for generating a signal having afrequency identical to that of said first radio signal and a signalhavinG a frequency identical to that of said second radio signal at athird point, means controlled by said third source for periodicallyproducing time reference signals, means for receiving said first radiosignal and said second radio signal at said third point, first phasecomparing means at said third point for comparing the phase of thereceived first radio signal with that of said signal having a frequencyidentical to that of said first radio signal, second phase comparingmeans at said third point for comparing the phase of the received secondradio signal with that of said signal having a frequency identical tothat of said second radio signal, means at said third point fordemodulating said first and said second radio signals to recover saidfirst time signal and said second time signal, and means for comparingrespectively said first time signal and said second time signal withsaid time reference signals.
 24. A position locating system according toclaim 23 wherein said first source, said second source and said thirdsource are respectively first, second and third atomic clocks.
 25. Aposition locating system comprising a first source of a signal of givenfrequency and given phase, a second source of a signal of said givenfrequency and a predetermined phase relationship with said given phase,a third source of a signal of said given frequency and a predeterminedphase relationship with said given phase, means controlled by said firstsource for transmitting a first radio signal from a first pointincluding first modulating means controlled by said first source forperiodically frequency shift modulating said first radio signal with afirst time signal, means controlled by said second source fortransmitting a second radio signal from a second point including secondmodulating means controlled by said second source for periodicallyfrequency shift modulating said second radio signal with a second timesignal, means controlled by said third source for generating a signalhaving a frequency identical to that of said first radio signal and asignal having a frequency identical to that of said second radio signalat a third point, means controlled by said third source for periodicallyproducing time reference signals, means for receiving said first radiosignal and said second radio signal at said third point, first phasecomparing means at said third point for comparing the phase of thereceived first radio signal with that of said signal having a frequencyidentical to that of said first radio signal, second phase comparingmeans at said third point for comparing the phase of the received secondradio signal with that of said signal having a frequency identical tothat of said second radio signal, means at said third point fordemodulating said first and said second radio signals to recover saidfirst time signal and said second time signal, and means for comparingrespectively said first time signal and said second time signal withsaid time reference signals.
 26. A position locating system according toclaim 25 wherein said first source, said second source and said thirdsource are respectively first, second and third atomic clocks.
 27. Aposition locating system comprising a first source of a signal of givenfrequency and given phase, a second source of a signal of said givenfrequency and a predetermined phase relationship with said given phase,a third source of a signal of said given frequency and a predeterminedphase relationship with said given phase, means controlled by said firstsource for transmitting a first radio signal from a first pointincluding first modulating means controlled by said first source forperiodically pulse modulating by pulsing said first radio signal with afirst time signal, means controlled by said second source fortransmitting a second radio signal from a second point including secondmodulating means controlled by said second source for periodically pulsemodulating by pulsing said second radio signal with a second timesignAl, means controlled by said third source for generating a signalhaving a given frequency related to that of said first radio signal anda signal having a given frequency related to that of said second radiosignal at a third point, means controlled by said third source forperiodically producing time reference signals, means for receiving saidfirst radio signal and said second radio signal at said third point,mixer means coupled to said means for receiving and responsive to saidfirst radio signal and to said second radio signal for producing a firstintermediate signal and a second intermediate signal, first phasecomparing means at said third point for comparing the phase of the firstintermediate signal with that of said signal having a given frequencyrelated to that of said first radio signal, second phase comparing meansat said third point for comparing the phase of the second intermediatesignal with that of said signal having a given frequency related to thatof said second radio signal, demodulating means at said third point forrecovering said first time signal and said second time signal, and meansfor comparing respectively said first time signal and said second timesignal with said time reference signals.
 28. A position locating systemaccording to claim 27 wherein said first source, said second source andsaid third source are respectively first, second and third atomicclocks.
 29. A position locating system comprising a first source of asignal of given frequency and given phase, a second source of a signalof said given frequency and a predetermined phase relationship with saidgiven phase, a third source of a signal of said given frequency and apredetermined phase relationship with said given phase, means controlledby said first source for transmitting a first radio signal from a firstpoint including first modulating means controlled by said first sourcefor periodically notch modulating said first radio signal with a firsttime signal, means controlled by said second source for transmitting asecond radio signal from a second point including second modulatingmeans controlled by said second source for periodically notch modulatingsaid second radio signal with a second time signal, means controlled bysaid third source for generating a signal having a given frequencyrelated to that of said first radio signal and a signal having a givenfrequency related to that of said second radio signal at a third point,means controlled by said third source for periodically producing timereference signals, means for receiving said first radio signal and saidsecond radio signal at said third point, mixer means coupled to saidmeans for receiving and responsive to said first radio signal and tosaid second radio signal for producing a first intermediate signal and asecond intermediate signal, first phase comparing means at said thirdpoint for comparing the phase of the first intermediate signal with thatof said signal having a given frequency related to that of said firstradio signal, second phase comparing means at said third point forcomparing the phase of the second intermediate signal with that of saidsignal having a given frequency related to that of said second radiosignal, demodulating means at said third point for recovering said firsttime signal and said second time signal, and means for comparingrespectively said first time signal and said second time signal withsaid time reference signals.
 30. A position locating system according toclaim 29 wherein said first source, said second source and said thirdsource are respectively first, second and third atomic clocks.
 31. Aposition locating system comprising a first source of a signal of givenfrequency and given phase, a second source of a signal of said givenfrequency and a predetermined phase relationship with said given phase,a third source of a signal of said given frequency and a predeterminedphase relationship with said given phase, means controlled by said firstsource foR transmitting a first radio signal from a first pointincluding first modulating means controlled by said first source forperiodically frequency modulating said first radio signal with a firsttime signal, means controlled by said second source for transmitting asecond radio signal from a second point including second modulatingmeans controlled by said second source for periodically frequencymodulating said second radio signal with a second time signal, meanscontrolled by said third source for generating a signal having a givenfrequency related to that of said first radio signal and a signal havinga given frequency related to that of said second radio signal at a thirdpoint, means controlled by said third source for periodically producingtime reference signals, means for receiving said first radio signal andsaid second radio signal at said third point, mixer means coupled tosaid means for receiving and responsive to said first radio signal andto said second radio signal for producing a first intermediate signaland a second intermediate signal, first phase comparing means at saidthird point for comparing the phase of the first intermediate signalwith that of said signal having a given frequency related to that ofsaid first radio signal, second phase comparing means at said thirdpoint for comparing the phase of the second intermediate signal withthat of said signal having a given frequency related to that of saidsecond radio signal, demodulating means at said third point forrecovering said first time signal and said second time signal, and meansfor comparing respectively said first time signal and said second timesignal with said time reference signals.
 32. A position locating systemaccording to claim 31 wherein said first source, said second source andsaid third source are respectively first, second and third atomicclocks.
 33. A position locating system comprising a first source of asignal of given frequency and given phase, a second source of a signalof said given frequency and a predetermined phase relationship with saidgiven phase, a third source of a signal of said given frequency and apredetermined phase relationship with said given phase, means controlledby said first source for transmitting a first radio signal from a firstpoint including first modulating means controlled by said first sourcefor periodically frequency shift modulating said first radio signal witha first time signal, means controlled by said second source fortransmitting a second radio signal from a second point including secondmodulating means controlled by said second source for periodicallyfrequency shift modulating said second radio signal with a second timesignal, means controlled by said third source for generating a signalhaving a given frequency related to that of said first radio signal anda signal having a given frequency related to that of said second radiosignal at a third point, means controlled by said third source forperiodically producing time reference signals, means for receiving saidfirst radio signal and said second radio signal at said third point,mixer means coupled to said means for receiving and responsive to saidfirst radio signal and to said second radio signal for producing a firstintermediate signal and a second intermediate signal, first phasecomparing means at said third point for comparing the phase of the firstintermediate signal with that of said signal having a given frequencyrelated to that of said first radio signal, second phase comparing meansat said third point for comparing the phase of the second intermediatesignal with that of said signal having a given frequency related to thatof said second radio signal, demodulating means at said third point forrecovering said first time signal and said second time signal, and meansfor comparing respectively said first time signal and said second timesignal with said time reference signals.
 34. A position locating systemaccording to claim 33 wherein said first sOurce, said second source andsaid third source are respectively first, second and third atomicclocks.